An incubating box includes a container with a flange, an inlet, holding portions, a space, protrusions and supports; a bed which is placed inside the space and supported by the protrusions, a retaining device which is arranged in the recess and supported by the pair of positioning plates, a water absorbing element which is laid down on a top face of the bed to cover the entire surface enclosed by the wall so that water from the water absorbing element is able to be distributed to every part in the bed; and a cap which has a peripheral skirt, a handle, ventilation holes and spacers, wherein the peripheral skirt extends downward to correspond to the flange of the container.